Design of an Absolute Shaft Encoder Using Optically Modulated Binary Code

Abstract

In order to avoid the fabrication of coding pattern over a shaft coupled disk of the binary coded absolute encoder, a new design concept has been presented in this paper. The proposed prototype can encode the binary information by optical modulation principle. Instead of lithographic fabrication, here the pattern code bits are implemented optically through a plurality of infra-red (IR) light emitting diodes (LED). Each LED transmits a bit of information as modulated optical signal and modulation is served by the principle of serial infra red control protocol. During the rotation of an object, a window position of the shaft coupled disk determines which bits’ information will be transmitted. Now, an IR detector of the receiver unit decodes this code by demodulating the transmitted signal. Finally, the absolute position of the object is evaluated from this code by searching a look-up table data. Thus, the receiver unit of the proposed encoder can sense the position of an object remotely without using any additional wireless device. Also, the sensing heads may not be damaged by the rotating disk vibration. The prototype has been tested by using De-Bruijn coding pattern and obtained promising results. Also, the proposed method is equally valid for any binary or gray pattern code.